HI Bill:

     I too have wondered about this process.  I have an O.S. .40S that has had three different rings in it and they all seem to fit the same. Perhaps all three fit quite well.

    Frank Bowman made the last two rings for me and what I think that I found was that I did not understand what a good fitting ring feels like.  The only engines that I have had much experience were McCoy engines circa 1950's and the K&B .40 circa 1975.  The MCoys always appeared to be very low on compression and were difficult to  start.  The K&B engine was a joy to use!

    All that I may suggest is that you run the engine in a rich 4 cycle for about 5 runs of about 5 minutes each  and then begin to lean it out for more runs but be careful to avoid any lean runs.  Fly the engine in a rich mode and watch the signs of overheating. I am speaking of the conventional ringed engines and not the more moderen Dykes rings. 

    My O.S..40S is going into a Green Box Nobler as the Nobler came out a bit tail heavy for the O.S. .35 that was planned for while the Nobler was being built.  Should have enough power! LOL

    Just use your engine in a gentle manner and if it is a quality engine, it should serve you a long time.  Oh yes, I use a fuel with a high content of Castor Oil.  Some like a fuel ithe 11% Castor Oil and 11% synthetic oil in ringed engines. I may try this blend in my O.S. in lieu of the all Castor Oil mix.

                                                                              Good luck and keep us posted on your progress.

                                                                              Frank

I don't have a lot of experience with rings but let me pass this along.

I had a ST51 "customized" with a new ring being part of that process.  The instructions stated that after less than an hour of run time, I should be able to see the ring "turning shiny."  Never happened.  Almost 2 hours of bench time, running as recommended, still never happened.  The most noticeable characteristic was the almost total lack of compression.

So I ended up sending the engine to Frank Bowman for a new ring (I couldn't get the sleeve and piston out).  After I got the engine back, I put an hour on the bench.  Still did not see appreciable "turning shiny" changes in the ring but, I now have compression.  It starts well and runs well.  I have yet to put it in an airplane and fly it but I have every confidence in the engine now whereas before I did not.

But remember, cylinder must be honed every time when you replace the ring. We do it in the only correct way, with a honing machine but I've heard that some people have used just a simple brake cylinder hone or even wet'n dry paper to re-do the crisscross pattern. It may work but real honing is the only way to keep it straight & round.

Define "correct". Is someone supposed to withdraw from a contest, or fly with an uncompetitive engine run that has suddenly lost power, just because they can't fix it "correctly"?

     The "honing" with a brake cylinder hone  mentioned above was incredibly brief and slow, and removed negligible metal. Just enough to cross-hatch the shiny spots. It did not make the cylinder shape change to any detectable degree (detectable meaning had negative long-term effects, and not measureable). It made it go from "worthless" to "competitive", which is ultimately all that matters. I wouldn't suggest it unless necessary,  but if your engine stops working, the chances of running across a Sunnen honing machine in the middle of a soybean field in Indiana are rather low.

    Replacing rings in the field, and roughing up the cylinder, was a routine event with the ST46 with factory rings or replacements. It's that, or lose. I think I will change the ring, rough it up with a brake cylinder hone, take my trophy, and apologize for not doing it "correctly" later.

    We are talking about pretty crude engines (it wouldn't be ringed otherwise) that had a strong propensity to suddenly go over the hill in various ways - lost power, erratic running, etc. You can probably always get it to run reliably, but not with good power.

     Using a brake cylinder hone is a last-ditch attempt that should never be done unless you have to,  but it fixes the problem.

    Brett

 But I see it as a mechanic who tries to do everything as well as possible. ST engines, and similar, are not like that.
 Maybe I'm spoiled away with my Schaublin machines and my contacts with the best and most innovative engine builders but I would never ever want to go through the field repairs you explained. I find it just amusing that something with such crap quality still determines what the majority thinks of ringed engines. I can say that we have gotten 100% rid of problems that you described. I am absolutely sure that a well prepared ringed piston/cylinder group is superior to ringless ABC or AAC in stunt engines.

Lauri
 

If and When you are sizing/fitting a newly chromed sleeve to a piston, it is essential to use a "real" precision hone, they keep the bore precise and round, that is worlds different to rebuilding an engine and re-ringing it, a cylinder hone works very well in that situation, as all you are doing is just breaking the surface slightly to add a cross-hatch  to the sleeve, this is essential in proper break in, what is as important is fitting the ring properly and know how, the materials used changes how you fit rings.
And as to the statement about a ringed aac being better... I don';t think so, It has no advantages and will not last as long as a properly done lap fit AAC.
If and when I do rings for my engine I am much happier with 2 rings pinned at opposing sides, I am never happy with an unpinned revolving rings If I can help it.

Randy

Thanks Randy.

I have 4 pistons coming for 2 cylinders so that leaves room for experimenting.. Anyway, Robbies chrome (or actually his late brother Bert's) is extremely good, one ring seems to last forever.
I'd like to try the Dykes ring. I got some samples from Frank but they are quite rough, I'd be better off making them myself.

Lauri